MOSCOW (AFP) - Russia hoped on Tuesday (May 3) that a new ceasefire could be announced within hours for Syria's battered city of Aleppo, where fresh fighting including rocket fire on a maternity hospital left at least 16 dead.

As the city was struck by some of its heaviest reported clashes in days, Russian Foreign Minister Sergei Lavrov said efforts were under way to agree to a freeze in the fighting.

"I am hoping that in the near future, maybe even in the next few hours, such a decision will be announced," Mr Lavrov told reporters after meeting UN Syria envoy Staffan de Mistura in Moscow.

France and Britain called for an urgent UN Security Council meeting on Aleppo, boosting the major push by world powers this week to end the fighting there.

"Aleppo is burning and it is crucial that we focus on this top priority issue," said British Ambassador to the UN Matthew Rycroft.

A Feb 27 truce between President Bashar al-Assad's regime and non-jihadist rebels raised hopes for efforts to resolve the five-year conflict.

But it has all but collapsed amid renewed fighting, especially in Aleppo.

A surge of violence that erupted on April 22 has killed more than 270 people in the divided northern city and undermined efforts to revive peace talks.

After a relative lull on Monday and early Tuesday, rebels in eastern Aleppo fired at least 65 rockets into government-controlled neighbourhoods, Syrian state news agency SANA reported.

At least three women were killed when the rockets hit Al-Dabbeet maternity hospital, state media said, and another 11 were killed in fire on other government-held districts.

The Syrian Observatory for Human Rights monitoring group said it had counted at least 19 dead and 80 wounded from the attacks on government-held areas.

Fierce fighting also raged on Aleppo's western edges after rebel groups detonated explosives in an underground tunnel, the correspondent said.

He said it was the most violent day for the city's regime-held west since clashes resumed 11 days ago.

New regime air strikes also hit rebel-held eastern areas in the afternoon, dotting the city with thick plumes of smoke, another AFP correspondent reported.

As warplanes thundered above, rebel groups and government forces exchanged nearly non-stop artillery fire.

Rescue workers said air strikes on eastern neighbourhoods killed at least two people.

The rocket attack on the maternity hospital was the sixth time a medical facility has been hit in 11 days in Aleppo, the International Committee for the Red Cross said, calling it "unacceptable".

The UN Security Council unanimously voted on Tuesday to condemn the targeting of health facilities in war zones.

In Moscow after seeing US Secretary of State John Kerry in Geneva on Monday, Mr de Mistura said it was crucial for Syria's ceasefire to be "brought back on track", hailing the February truce as a "remarkable achievement".

Diplomatic efforts were set to continue on Wednesday in Berlin with Mr de Mistura joining the German and French foreign ministers for talks with Syria's main opposition leader.

The German foreign ministry said their discussions would focus on how to reduce violence and improve Syria's humanitarian situation so peace talks can resume.

On Monday, Mr Kerry said the situation in Syria was "in many ways out of control and deeply disturbing".

Washington and Moscow are working together to include Aleppo in a so-called "regime of silence" - a freeze in fighting - aimed at bolstering the broader truce brokered by both world powers.

The two countries have agreed to boost the number of Geneva-based truce monitors to track violations "24 hours a day, seven days a week," Mr Kerry told reporters.

"We're trying to press this as fast as possible but I don't want to make any promises that can't be kept," he told reporters after meeting Mr de Mistura and Saudi Foreign Minister Adel al-Jubeir, whose government has influence with key rebel groups.

In a nod to Moscow's demands, Mr Kerry said Washington would press moderate rebels to separate themselves from Al-Nusra Front jihadists in Aleppo.

Russia and Mr Assad's regime have used the presence of Al-Nusra, an affiliate of Al-Qaeda which was not party to the February ceasefire, as an excuse to press their offensive.

The Observatory says more than 270 civilians - including 54 children - have been killed on both sides of divided Aleppo since April 22.

The city was initially excluded from a deal announced last week to "freeze" fighting along two major fronts in the north-west and in Eastern Ghouta near Damascus.

Syria's conflict erupted in 2011 after anti-government protests were put down, and escalated into a multi-faceted war that has killed more than 270,000 people and forced millions from their homes.